This invention relates to devices that may be used for closure of circular conduits such as pipes, shafts and access openings for storm drains, sewer access manholes, utility equipment vaults and the like that may be located in the ground. The new closure device may be positioned and secured in a conduit to inhibit entry of debris that may be produced as a result of construction work or other activity when other closure devices have been removed or may be.
Devices for closure of circular conduits have been in use for many years. A well known device, the manhole cover, that may be made of metal is typically used to cover a conduit opening at street level to close opening access to sewers, underground equipment vaults, storm drains and other underground facilities such as valve control access enclosures and the like. Other closure devices may have been designed to temporarily or permanently close or partially close conduit openings such as storm drains to filter debris from entering fluids to avoid clogging the drain system. The conduit with opening may be generally vertical or may be other than vertical yet a closure device may be necessary to inhibit entry of debris or other matter when the conduit opening is not being used for access entry or other intended purposes. For example, when a street may be repaired, often the manhole covers may be removed and the access opening covered with street level metal plates. However, these temporary coverings may be unintentionally moved allowing debris to fall into the conduit and for example into the sewer.